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Arrays

Arrays

• (^) Review of java data types
• (^) As we discussed in the previous lessons, data types is a set of

data values, along with a set of operations on those values.

• (^) Integer, real, character and Boolean data types are said to be

atomic because they have no component parts that can be

accessed separately.

• (^) For example a single character is atomic, but the string

“Good Morning” is not atomic because it is composed of 12

characters.

• (^) In a composite data type, each value is a collection of

component items.

• (^) The entire collection is given a single name, yet each component

can still be accessed individually.

• (^) The class is an example of composite data type.
• (^) A class has a name and can be composed of named data fields

and methods.

• (^) The data fields and methods can be accessed individually by

name.

• (^) A class is unstructured because access does not depend on an

ordering relationship among the data fields or the methods.

• (^) That is, if we change the order in which the members of the class

are listed, this change has no effect on how we access them.

• (^) For example, here is the same class, declared with its data fields in two different order: class Example { int field1; int field2; double field3; } class Example { double field3; int field2; int field1; }

What is an array

• (^) Arrays are data structures consisting of related data items of the same type.
• (^) Thus, an array is a group of variables or containers that is given only one name.
• (^) The group of variables are placed under a single umbrella with only one name.
• Arrays make it convenient to process related groups of values or values of the same type.
• (^) Arrays remain the same length once they are created.

• (^) Each variable in the group that makes up an array is called elements or components.
• (^) An array element is given a number to make references to it instead of a name.
• (^) An array is a variable that contains other variables of values that are all of the same type.
• (^) Arrays are objects, hence, they are considered as reference data types.
• (^) However, the elements of an array can be of either a primitive type or reference type.

Declaring an Array

• (^) Syntax for one dimensional array declaration
  • (^) Data-Type[] Array-Name;
  • Data-Type describes what is stored in each component of the array
  • (^) The brackets following Data-Type indicate that this structure is an array of Data-Type elements.
  • (^) ArrayName is a location in memory that will hold the address of an array when that array is instantiated.
  • (^) For example,
    • (^) int[] numbers;

Creating/instantiating an

array

• (^) You create an array just like you create an object; you use new.
• Following is the syntax template for instantiating an array.
• (^) Notice that arrays don’t need to be initialized, so we don’t pass a list of arguments.
• (^) Instead, we put the number of slots to be in the array in brackets beside the type of the array.
• (^) Syntax for creating one dimensional array
• (^) Array-Name = new Data-Type[Int-Expression];

• (^) The angle array has four components, each capable of holding one float value.
• (^) The testScore array has a total of ten components, all of type int.

• (^) Java provides an alternative syntax for declaring an array variable.
• (^) You can place the brackets that signal an array after the array name, as shown here:
• (^) char letters[];
• (^) char upperCase[];
• (^) char lowerCase[];

• (^) Look closely at this example: letters and upperCase are composite variables of type char[], but lowercase is a simple variable of type char.
• (^) If you use the syntax that we introduced first, you cannot forget to put the brackets on one of the array identifiers:
• (^) char[] letters, upperCase, lowerCase;

• (^) Java also provides an alternative way to instantiate an array.
• (^) You learned previously that Java allows you to initialize a variable in its declaration:
• (^) int delta = 25;
• (^) The value 25 is called an initializer.
• (^) You can also initialize an array in its declaration, using a special syntax for the initializer.
• (^) In this case,you specify a list of initial values for the array elements, separate them with commas, and enclose the list within braces:
• (^) int[] age = {23, 10, 16, 37, 12};

Accessing Individual

Components

• (^) To access an individual array component, we write the array name, followed by an expression enclosed in square brackets.
• (^) The expression specifies which component to access.
• (^) The syntax template for accessing an array component follows:
• (^) Array-Name[Index-Expression]